Photoelectric cell circuit



Aug. 9, 1938. w. N. GOODWIN, JR Re. 20,823

PHOTOELECTRIG CELL C IRCUIT Original Filed June 23, 1933 eiscued Aug. 9,1938 p Re. 20,823

UNITED STATES PATENT OFFICE I 2cm wum lafiffi N. 1., u-

Jenn

This invention relates to circuits for photolectric cells oi the flatdisk or barrier layer type, d more particularly to measuring relaycircuits n which the direction and magnitude of current ow are to dependupon a diil'erence in the light I tensities at two cells oi the barrierlayer type.

It has been found impractical to connect cureat-generating photoelectriccells of the barrier layer type diilerentially in series opposition,that is, in a single series circuit including two cells and a currentresponsive device, the circuit conections being such that the voltagegenerated in one cell directly opposes that generated in the other. Thisarises from the fact that the voltage and resistance characteristics ofthese cells are ail'ected by temperature and other effects. Since eachcell works into the other, the current output of each is not determinedsolely by the light intensity at that cell but varies with the voltageand resistance of the second cell. On the other hand, the currentgenerated in a relatively low resistance circuit is practicallyindependent oi temperature conditio and is stable. For this reason, eachcell mus be so connected in a relatively low resistance circuit, and thecircuits so arranged that the effects of the currents can bediilerentially combined in opposition.

An object of the invention is to provide a sensitive and stablephotoelectric cell circuit including a pair of cells of the barrierlayer type and a current response member subjected to the diil'erentialaction of currents generated by the cells. A further object is toprovide a circuit of the type stated, and in which current generated byone cell may flow in a circuit which does not include the other cell.More particularly, an object is to provide a relay system including apair of photoelectric-cells of the barrier layer type and a'relay, theelectrical network of said cells including a common path or branch inwhich the relay is located and in which the separate cells tend toestablish current flow in opposite directions, and other branches whichcomplete a series circuit for each cell.

These and other objects and advantages of the invention will be apparentfrom the following specification when taken with the accompanyingdrawing, in which:

Fig.1 is a circuit diagram of an embodiment of the invention which isappropriate for a determination of the relative illumination of twophotoelectric cells;

Fig. 2 is a fragmentary circuit diagram of a relay circuit embodying theinvention; and

signer to Weston Electrical Instrument Corporatlon, Newark, N. 1., acorporation or New Original No. 2,032,010, dated February 25, 1938,Serial No. 877,332, June 23, 1833. Application for reissue February 10,1933, Serial No. 189,905

12 Claims. 250-415) Figs. 3 and 4 are circuit diagrams of measuringsystems embodying the invention.

In the drawing, the reference numerals l, 2, identify two photoelectriccells of the direct action or barrier layer type, the cells beingusually of similar design and operating characteristics. The cells aresubjected to illumination from two different sources or to light raysreaching the cells from the same source but by different paths. As

represented diagrammatically in the drawing, this condition of unequalillumination may obtain when the cells I, 2 are illuminated by separatelight sources 3, 4, respectively, a shield 5 being positioned to preventa cross-illumination of the cells. I

A measuring instrument 6 is a series element in the lead I that connectssimilar electrodes 8 of the two cells, and the other pair of similarelectrodes 9 are joined by a lead Ill. It will be noted that leads I andI0 complete a series circuit which includes the cells and instrument,the cells being oppositely arranged in the circuit and thereby tendingto establish current flow in opposite directions.

In accordance with the invention, additional circuit elements areprovided to complete relatively independent circuits for each cell. Asillustrated, a resistance II is shunted across the measuring instrument,and an adjustable tap I! on the resistance is connected to the lead l0through a connection l3. If desired, a scale It may be provided toindicate, on some convenient system of graduations, the setting of thetap I2 along resistance II.

The added circuit elements cooperate with the original series circuit toform a plurality of loop circuits which have portions in common, but inwhich the cells are in the non-common portions of diflerent loopcircuits. When either cell is darkened, the resistance of the loopcircuit of that cell is very high, but the loop circuit of the othercell provides a relatively low resistance path for current flow inaccordance with the illumination at the other cell.

The tap I2 is adjustable over resistance II to balance the currentoutput from the two cells, but not their output voltages, by regulatingthe magnitude of the sections or resistance II which are included'in thetwo loop circuits. This operation does not involve a comparison of theresistances of the photocells or a comparison of the values of the twosections into which resistance II is divided by the tap i2, since thecircuit does not have the general form of and does not function as aWheatstone bridge. The

electro-motive forces from self-generating cells are balanced againstthose diflerences oi poten tialacrossresistorswhichareproducedbycurrentsfrom the respective cells. The circuit elements which divide the mainseries circuit into loop circuits are passive, i. e., do not includebatteries or other sources oi current which are essential ior Wheatstonebridge operation.

When the system includes a measuring instrument or galvanometer 5, theapparatus may be employed for brilliancy, on or opacity measurements,and the substitution oi a relay for the instrument permits the automaticoperation of mechanism in accordance with variations in these factors.

In the relay system shown in Fig. 2, the general circuit arrangement is,or may be, substantially identical with that 01' Fig. 1, except that themoving coil l5 oi a'relay is connected in lead I, the relay including acontact arm I which is movable between contacts II, II to close acircuit including a current source I! and. respectively, the responsivedevices 20 or 2|. By adjusting the tap I! to bring the contact arm I.into its neutral position when the cells develop equal currents, orcurrents bearing a predetermined ratio to each other, a departure ineither sense from that initial condition of illumination and resultingcurrent ilow will result in a deflection of contact arm it towards oneor the other of contacts II, It.

The circuit shown in Fig. 3 provides a simple and efliclent instrumentarrangement for measuringthe relative illumination of the photoelectriccells I, 2. Like electrodes 8 of each cell are connected by leads I tothe separate coils olcoil sections of a measuring instrument 8', and thecommon junction of the coils is connected by lead II to the jumper orcommon lead ll of the other pair 01' like electrodes 9 oi the cells. Thesections of the instrument coil are so positioned that the deflection oithe pointer varies as the ratio of the currents generated by theseparate cells.

In the similar measuring circuit of Fig. 4, the two sections of themoving coil system are so positioned that currents flowing from the twocells, as indicated by the arrows, exert opposite eilects upon themotion of the complete coil system, and the resulting deflection isproportional to the difl'erence in the current outputs of the two cells.As with the other forms of the invention, it is to be noted that thepath of current flow of each cell does not include the other cell.

' The exact circuit arrangement 0! 1 networks embodying the invention issubject to e variation, so long as the current responsi device islocated in a branch oi the network in which currentflow from the twocells tends to establish opposite eflects, and the cells are located inthe non-common portion of two loop circuits which have at least aportion in common.

I claim:

1. In a photoelectric cell circuit, a pair of photoelectric cells oi thebarrier layer type. a current responsive device, and a networkconnecting I said cells anddevice to subject said device to thediil'erential action of currents generated by the said cells; saidnetwork including a main series circuit comprising circuit elementsjoining one set of like terminals of said cells and connecting thedevice between the other set oi like terminals, and means forming ashunt path dividing said main series circuit into two loop circuitshavterminal oi said winding is maintained at the rler layer typephotoelectric cells, a current reing the cells in the non-commonportions of th respective loop circuits, said means consisting passivecircuit elements connected between the joined terminals of said cellsandsaid device.

2. A photoelectric cell circuit as claimed in claim 1, wherein saidcurrent responsive devi comprises a measuring instrument having a movingcoil formed in two sections, the respective sections being located innon-common portions of the two loop circuits.

3. In photoelectric apparatus for measuring the diilerence in theillumination at two points, a pair of barrier layer photoelectric cellsadapted to. be positioned at the said two points, a direct conductiveconnection between one set of like terminals of said cells, a currentmeasuring instrument having an operating winding comprising two sectionshaving a terminal in common circuit elements completing a series circuitincluding both cells and both sections or said operating winding, and alead connecting the common terminal of said operating winding to saidconductive connection, whereby the common common potential of the set oflike cell terminals which are joined by said conductive connection.

4. In a photoelectric cell circuit, a pair of barsponsive device, leadsconnecting said cells to said device to subject the same to the opposinginfluence of currents generated by the separate cells, and additionalcircuit elements of passive type forming a path of current flow for eachcell which is substantially independent of the other cell.

5. In apparatus of the type stated, a pair of photoelectric cells of thebarrier layer type and each having a pair oi electrodes, a currentresponsive device connected between similar electrodes of said pair 01'cells, a lead connecting the other electrodes of said cells, aresistance shunting said device, and a passive connection from a pointon said resistance to said lead.

6. Apparatus as claimed in claim 5, wherein said connection includes atap adjustable along said resistance. a

7. Apparatus as set forth in claim 5, wherein said device is a currentmeasuring instrument.

8. Apparatus as set forth in claim 5, wherein said device is a relay,and said relay includes a contact arm movable in response to thedifference of the currents generated by said cells, and a contactadapted to be engaged by said contact arm.

9. A device of the character described comprising a plurality of spacedlight-sensitive means capable oi generating an electric current,electrically actuated means connected to each 01 said light-sensitivemeans in such manner that the current from one light-sensitive meansopposes that from another, and means adapted to be actuated by saidelectrically actuated means when the amounts of current generated by twoof the lightsensitive means are unequal.

10. A photoelectric control system comprising a pair oi photoelectriccells of the barrier layer type, a current relay having relativelymovable contacts, circuit means connecting said cells and relay tosubject said relay to opposing effects of currents generated by therespective cells, and controlled means having a circuit in which saidrelay contacts are included.

11. In apparatus for photoelectric measurement, control and the like,the combination oi a pair of photoelectric cells of the barrier layer m.a current responsive device, and circuit eleents. connecting said deviceto said cells to niiuence said device in accordance with the diferencein the current outputs of the two cells; d network including for eachcell a circuit that flectively excludes the other cell and includesistan'ce.

12. In apparatus, for photoelectric measure-- ment. control and thelike, the combination ot a pair of photoelectric cells of the barrierlayer type. circuit elements forming for each cell a closed circuit inwhich the current flow established by that cell is substantiallyindependent of the other cell, said closed circuits each includingresistance means across which a potential drop appears when current flowis established in that circuit by the associated cell, and a currentresponsive device connected to said resistances to subject the device toa current flow that varies with the difference in the current outputs ofthe two cells.

WM. NELSON GOODWIN, J a.

